1. Technical Field
The present invention relates to a transportation device that transports a transportation target material such as paper that is used for printing or the like, for example, and a recording apparatus including the transportation device.
2. Related Art
There has been known an existing ink jet printer that ejects ink onto recording paper (transportation target material) from a recording head (recording unit) so as to form an image, as one type of recording apparatuses (for example, JP-A-2007-217176).
In the printer as disclosed in JP-A-2007-217176, surface character of the recording paper that is transported is captured as continuous images by a camera and captured two adjacent before and after (hereinafter “adjacent”) images are compared in the chronological order. Then, movement amounts of a focused pattern in the respective images are figured out and integrated so as to calculate an actual transportation amount of the recording paper.
In this case, images in accordance with relief of the surface of the recording paper illuminated by a light emitting element appear on the two captured images by the camera. Based on this, illuminating an image capturing region by the camera on the surface of the recording paper as even as possible contributes to improvement of calculation accuracy of an actual transportation amount of the recording paper.
Also, there has been known an image forming apparatus (recording apparatus) including an illumination device that is configured to reduce luminance unevenness of a light irradiation surface of a document (transportation target material) that is irradiated with light by the light emitting element such as a light emitting diode (LED) (for example, JP-A-2010-183497). That is to say, in the image forming apparatus as disclosed in JP-A-2010-183497, a plurality of light emitting elements are arranged at both sides of the recording paper that is transported in the sub-scanning direction (transportation direction) of the recording paper such that optical axes thereof are inclined with respect to the sub-scanning direction of the recording paper when seen from the above. With this, the luminance unevenness of the light irradiation surface of the recording paper is made to be reduced.
When the illumination device as disclosed in JP-A-2010-183497 is mounted on the printer as disclosed in JP-A-2007-217176, luminance unevenness of the image capturing region by the camera on the surface of the recording paper is reduced. However, the image capturing region of the recording paper is irradiated with light by the light emitting elements arranged at the transportation direction side of the recording paper. Therefore, a distance between the light emitting elements and the image capturing region is different between adjacent two images that are captured by the camera.
Therefore, an appearing shadow shape based on the relief of the image capturing region on the surface of the recording paper is different between the adjacent two images that are captured by the camera. Due to this, error of the movement amounts of the focused pattern in the respective images is increased, resulting in a problem that the detection accuracy of the actual transportation amount of the recording paper is lowered.